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  Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770


  Postscript device settings for "pixel perfect" matching to screen plot layout

Calling Sequence



  PXPERFECT is designed to achieve nearly "pixel perfect" matching
  of plot layout when rendering a plot on the IDL Postscript device.
  The dimensions and character sizes of the current display device
  are used to construct a group of settings which can be passed to
  the Postscript device driver using the DEVICE procedure.
  The key capability of PXPERFECT is to determine the size of fonts
  to match the on-screen size. Once this size is determined, IDL
  will adjust other Postscript output dimensions such as plot
  margins, font sizes, symbol sizes, etc, to match exactly the
  on-screen layout.
  The current direct graphics device must be a screen display
  device, such as 'X' or 'WIN'. The user wouuld first call
  PXPERFECT() to determine what the appropriate settings for the
  Postscript device would be. At a later time, the user may switch
  to the Postscript device to render the plot for output.
  This is the approximate order of calling:
    ;; Prerequisite: current graphics device is display device
    SET_PLOT, 'X' ;; or 'WIN'
    TF = 1.0 ;; Thickness factor (see "Dealing with line thickness" below)
    ;; User adjusts the plot layout to taste
    PLOT, ... data ..., thick=1.0*TF
    ;; Capture layout settings and then initialize Postscript
    SET_PLOT, 'PS' ;; NOTE: PXPERFECT() called *before* SET_PLOT
    ;; User calls same plot command(s) with no changes to layout
    PLOT, ... data ..., thick=1.0*TF
    ;; Close output plot file
  If the display window is resized, then PXPERFECT should be called
  again to capture the new layout settings.
  The value returned by PXPERFECT is an IDL structure, with fields
  that are meant to be passed to the IDL Postscript driver using the
  DEVICE, _EXTRA=(...) statement.
  Output Page Size. The dimensions of the Postscript output page
  will be set so that the output page exactly matches the displayed
  plot window. The algorithm does assume that the user's display
  density settings are correct, in particular, that !D.X_PX_CM is a
  correct reflection of the number of screen pixels per centimeter.
  The user can adjust the output page size in several ways.
  PXPERFECT accepts the XSIZE, YSIZE and SCALE_FACTOR keywords and
  interprets them in the same way that the standard procedure DEVICE
  does. In order to maintain the same layout, the user may specify
  XSIZE or YSIZE, but not both. If both XSIZE and YSIZE are
  specified, then the aspect ratio of the output page will not match
  the on-screen display window, and pixel-perfect layout matching
  cannot be attained in that case.
  Dealing with Line Thickness. The Postscript device has a
  different base line thickness compared to most on-screen display
  devices. The value returned in the THICK_FACTOR keyword is a
  scale factor which should be multiplied by all thicknesses when
  rendering to Postscript.
  Thus, if the desired on-screen line width is 2.0 units, then the
  Postscript line thickness will be 2.0*TF, where TF is the value
  returned in the THICK_FACTOR keyword.
  Passing Other Keywords to DEVICE. PXPERFECT() accepts all the
  keywords that the DEVICE procedure accepts. Any keywords that do
  not specifically affect PXPERFECT's operation are passed
  along to the output structure, and hence to DEVICE.

Positional Parameters


Keyword Parameters

  INCHES - set this keyword if Postscript dimensions are to be
            specified in inches instead of centimeters. This keyword
            also specifies the units of the user-passed keywords
            Default: not set (i.e. centimeter units)
  LANDSCAPE - set this keyword to indicate landscape orientation instead
              of portrait orientation.
              Default: not set (i.e. portrait orientation)
  SCALE_FACTOR - a unitless scale factor which is used to scale the
                  size of the Postscript page output. By default the
                  output page size in inches or centimeters is scaled
                  to match the on-screen size. Use this keyword to
                  increase (>1.0) or decrease (<1.0) the size of the
                  output page.
                  Default: 1.0
  THICK_FACTOR - upon output, THICK_FACTOR, which contain a factor
                  which should be used to multiply all line width
  XSIZE, YSIZE - user-requested output page size which may differ
                  from default Postscript page size. The user should
                  specify either XSIZE or YSIZE, but not both;
                  specifying both will cause the output page layout to not
                  exactly match the on-screen graphic layout. Also,
                  XSIZE or YSIZE override the SCALE_FACTOR keyword.
                  Default: not set (i.e. output page size will match
                  on-screen size)
  XOFFSET, YOFFSET - user-requested page offsets.
                  Default: plot at origin (landscape plots are
                  adjusted appropriately)


  PXPERFECT returns a single IDL structure, which is meant to be
  passed to the IDL Postscript device. This structure is passed
  using the DEVICE procedure and the _EXTRA mechanism.

Side Effects

  The graphics device must be set to a screen display device when
  PXPERFECT is called.
  Upon the first call to PXPERFECT, the graphics device is
  momentarily switched to 'PS' in order to retrieve Postscript
  device settings.


  ;; Plot to screen display
  PLOT, FINDGEN(10), charsize=1.5
  ;; Initialize Postscript
  DEVICE, _EXTRA=PS, FILENAME='outfile.ps'
  ;; Same plot, to Postscript page
  PLOT, FINDGEN(10), charsize=1.5
  ;; Finish output

See Also


Modification History

  Written, CM, 2010
  Documented, CM, 2011-04-15
  Square bracket array notation, CM, 2011-12-21

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